Copper in trace amounts is essential to life. It is also toxic, when the excess over physiologic requirements that is present in almost every diet, accumulates. The mammalian liver is the central organ for the maintenance of copper homeostasis and is also the primary target for its toxic effects. Copper balance is achieved by the interplay of uptake by hepatocytes, incorporation of the metal into cellular and secretory proteins, storage in lysosomes and the excretion of the excess via the bile. Defective biliary copper excretion, either intracellular or extracellular, results in copper retention. To obtain a better understanding of the mechanisms by which copper is retained and thus capable of exerting its toxic effects, this project will investigate the hypothesis that failure of an intracellular agent capable of controlling the biliary excretion of copper or sequestering it in an innocuous form, results in hepatocellular injury. A novel, low molecular (~10 kDa) copper-binding protein, Cuprophylin (CPP), was isolated in reactivity with a specific antibody and its variable metal content distinguish it from metallothionein. The goal of this project is to elucidate the nature; the regulation; the role in cellular copper trafficking, excretion and sequestration; and the pathologic significance of CPP. The identity of CPP will be established by amino acid and DNA sequencing studies and the role of metals in its regulation will be investigated in cell models of human hepatoblastoma cell lines. A possible role as a biliary copper transporter will be defined by studying the excretion of radiocopper labeled CPP in cannulated rat bile. The topography of the distribution of CPP in normal and disease livers will be studied immunocytochemically and the role of lysosomes in causing defective biliary excretion will be explored. Results of these studies will provide a better understanding of the abnormality responsible for the phenotypic expression of the genetic defect which results in Wilson's disease and possibly elucidate the pathogenesis of Indian childhood cirrhosis and idiopathic copper toxicosis ("Western" or "non-Indian" Indian childhood cirrhosis).